Systems and methods for powering circuits for a communications interface

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part and claims the priority benefit of U.S. patent application Ser. No. 11/820,745 entitled “Apparatus and Method for Recovery of Wasted Power from Differential Drivers” by Hongwu Chi and filed on Jun. 19, 2007, which is a continuation-in-part of U.S. patent application Ser. No. 11/800,861 entitled “Apparatus and Method for Termination Powered Differential Interface Periphery” by Hongwu Chi and filed on May 7, 2007, both of which are incorporated herein by reference. This application also claims the priority benefit of U.S. Provisional Application No. 60/997,853 entitled “Systems and Methods for Powering Circuits for a Communications Interface” by Hongwu Chi and filed on Oct. 5, 2007, which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates, in general, to the field of powering electronic components. In particular, the present invention relates to powering circuits for a communications interface.

2. Related Art

In a typical data communications system, a transmission line between a transmitter and a receiver is biased at an intended voltage using biasing circuitry. The biasing circuitry may be configured to draw current from a power supply to produce a voltage drop between the power supply and the transmission line. Alternately, the biasing circuitry may be configured to draw current from a power supply to produce a voltage drop between the transmission line and a ground node or power sink. The current drawn from the power supply is typically not used for another purpose in the data communications system. Power is therefore consumed by the data communications system to maintain the voltage bias.

SUMMARY

There is a need to minimize power consumption of electronic circuits such as those used in a data communications system. By minimizing power consumption of electronic circuits, energy can be conserved. In electronic circuits powered by a battery, reducing power consumption lengthens battery life. Reducing power consumption can also reduce energy expenses. Power consumption of electronic circuits such as those used in a data communications system may be minimized by a system including an electronic circuit configured to power another electronic circuit, or using a method of powering an electronic circuit using another electronic circuit.

Various embodiments of the invention enable power that is first used to establish bias conditions at a transmission line or transmission line driver circuitry to be further used to power additional electronic circuits. By using power first used to establish bias conditions for additional purposes, overall power consumption is reduced compared to the prior art.

A communications interface is provided including transmitter circuitry and a power supply configured to at least partially power the transmitter circuitry. The transmitter circuitry is configured to transmit data over a transmission line to a receiver module. The power supply is configured to use current received from the receiver module over the transmission line to at least partially power the transmitter circuitry.

An electronic circuit is provided including a current regulator and a voltage regulator. The current regulator is configured to sink a current regulated to be approximately constant. The voltage regulator includes a power output and is configured to regulate a voltage of the power output to be approximately constant. The voltage regulator is configured to receive the current sinked by the current regulator from the current regulator, and supply the current sinked by the current regulator to another electronic circuit through the power output.

An electronic circuit is provided including transmission line driver circuitry coupled with a transmission line. The transmission line is coupled with a first power supply through an impedance. The electronic circuit also includes digital data circuitry coupled with the transmission line driver circuitry and configured to transmit data over the transmission line using the transmission line driver circuitry. The digital data circuitry is configured to receive power from a second power supply. The electronic circuit further includes current regulator circuitry coupled with the transmission line driver circuitry and configured to regulate a current received from the first power supply through the transmission line driver circuitry to be approximately constant. The electronic circuit additionally includes voltage regulator circuitry coupled with the current regulator circuitry and configured to provide a second power supply having an approximately constant voltage. The second power supply supplies current received from the first power supply through the current regulator circuitry to at least the digital data circuitry.

A system for data communications is provided including data communications transmitter circuitry, biasing circuitry, and voltage regulator circuitry. The data communications transmitter circuitry is configured to transmit data via a transmission line. The biasing circuitry is configured to bias the transmission line at a bias voltage by sinking current from a first power supply. The voltage regulator circuitry is coupled with the biasing circuitry and configured to regulate an approximately constant voltage at a second power supply. The second power supply is coupled to the data communications transmitter circuitry. The voltage regulator circuitry is further configured to supply current sinked by the biasing circuitry from the first power supply to the data communications transmitter circuitry via the second power supply.

A method for powering circuits for a communications interface is provided including biasing a transmission line using biasing circuitry, sinking current from a first power supply through the biasing circuitry, and regulating a voltage of a second power supply to be approximately constant. The biasing circuitry is coupled with the transmission line and configured to draw current from the first power supply. The second power supply is configured to power circuitry for the communications interface. Current is sinked from the first power supply to be supplied to the circuitry for the communications interface via the second power supply.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram illustrating a communications interface.

<figref idref="DRAWINGS">FIG. 2</figref> is a schematic diagram illustrating communications interface circuitry.

<figref idref="DRAWINGS">FIG. 3</figref> is a block diagram illustrating an exemplary communications interface configured to re-use current from biasing a transmission line and/or driver circuitry to power a communications transmitter.

<figref idref="DRAWINGS">FIG. 4</figref> is a block diagram illustrating an alternative embodiment of a communications interface configured to re-use current from biasing a transmission line and/or driver circuitry to power a communications transmitter.

<figref idref="DRAWINGS">FIG. 5</figref> is a schematic diagram illustrating communications interface circuitry configured to re-use current from transmission line biasing circuitry to power communications transmitter circuitry.

FIG. .<b>6</b> is a schematic diagram illustrating exemplary circuitry configured to re-use current from biasing circuitry as a second power supply.

<figref idref="DRAWINGS">FIG. 7</figref> is a block diagram illustrating DC-coupled communications interface circuitry configured to re-use current from transmission line biasing circuitry to power communications transmitter circuitry.

<figref idref="DRAWINGS">FIG. 8</figref> is a block diagram illustrating AC-coupled communications interface circuitry configured to re-use current from transmission line biasing circuitry to power communications transmitter circuitry.

<figref idref="DRAWINGS">FIG. 9</figref> is a flowchart of an exemplary method for powering circuits for a communications interface.

DETAILED DESCRIPTION

The present invention includes, in various embodiments, systems and methods of powering a data communications interface. The communications interface may be configured to communicate digital data provided at a transmitter module input port at one end of a transmission line such that the digital data is output at a receiver module output port on an opposite end of the transmission line. The digital data may be transmitted for display on a video display and/or audible reproduction via an audio amplifier. The communications interface may include electronic circuits that consume electrical power by passing electrical current through active and passive electronic devices while communicating the digital data. The communications interface may be representative of a high-definition multimedia interface (HDMI) transmission system, Digital Visual Interface (DVI) transmission system, DisplayPort transmission system, or the like. For example, a transmitter input port may be coupled with electronics within an audio/visual source such as a digital versatile disc (DVD) player, and a receiver output port may be coupled with electronics within an audio/visual display unit such as a high definition television (HDTV) set.

Various embodiments of the systems and methods described herein may be used within HDMI transceivers, DVI transceivers, and DisplayPort transceivers. The embodiments may enable these systems to have lower overall power dissipation, longer battery life, reduced cooling requirements, and smaller form factors. Lower power dissipation may become increasingly important as transmission data rates increase, as increasing data rates typically are accompanied by increasing power dissipation. For example, embodiments may be used in systems with transmission data rates equal to or greater than approximately 1 megabit per second (Mbps), 10 Mbps, 100 Mbps, 250 Mbps, 500 Mbps, 1 gigabit per second (Gbps), 1.5 Gbps, 1.62 Gbps, 1.65 Gbps, 2 Gbps, 2.2 Gbps, 2.7 Gbps, 3.4 Gbps, 4.46 Gbps, 4.95 Gbps, 10 Gbps, 10.2 Gbps, 10.8 Gbps, or greater. The digital data may be transmitted over a transmission line at least partially incorporated within a length of cable between a transmitter module and a receiver module. The length of cable may be greater than approximately 10 centimeters (cm), 90 cm, 150 cm, 250 cm, 300 cm, 500 cm, 600 cm, 750 cm, 900 cm, 10 meters (m), or 12 m.

Applications-for embodiments of the present invention may include portable electronics, including, but not limited to, cellular telephones, portable media players such as music players (e.g., MP3 players), video players (e.g., MP4 players), handheld computers and PDA's, gaming consoles, handheld electronic games, and portable memory storage devices (e.g., USB thumb drives or jump drives). Electronic circuits including embodiments of the present invention may also be used within audio/visual entertainment systems such as DVD players, Blu-Ray video players, HD-DVD players, personal video recorders and digital video recorders, digital still cameras, video cameras, etc. Other devices that may include the electronic circuits may also include personal computers, laptop computers, computer networking equipment, data communications equipment, and telecommunications equipment. The embodiments may also be used in many devices not listed herein.

The data communications interface may include transmitter circuitry that is powered using current that is first used to establish a predetermined voltage, or a bias point, at a transmission line between the data communications transmitter circuitry and data communications receiver circuitry. Biasing circuitry may be used to set an appropriate operating point for the data communications transmitter circuitry and/or data communications receiver circuitry such that the data communications transmitter circuitry and/or data communications receiver circuitry operate within certain desired parameters. The biasing circuitry may also be used to establish a predetermined current through the transmission line between the data communications transmitter circuitry and the data communications receiver circuitry.

In some embodiments, current supplied to the transmitter module from the biasing circuitry is re-used to power the data communications transmitter circuitry. As a result, the data communications transmitter circuitry can be operated using less power overall than the prior art. For example, without re-using power, a transmitter module and associated circuitry may consume approximately 300 milliwatts (mW) of power while transmitting video data at a 720 p or 1080 i resolution according to an HDMI standard. On the other hand, an HDMI transmitter module including an embodiment of the present invention may dissipate less than 50 mW of power while transmitting video data at a 720 p or 1080 resolution. The HDMI transmitter including an embodiment of the present invention may dissipate less than 100 mW of power while transmitting video data at a 1080 p resolution. The HDMI transmitter may support link data rates up to 165 million pixels per second (Mpixel/sec). Lower power operation is achieved by re-using the current first used in biasing the transmission line for a second purpose, which is to provide power to the data communications transmitter circuitry.

<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram illustrating a communications interface <b>100</b>. The communications interface <b>100</b> includes a transmitter module <b>102</b>, a transmission line <b>104</b>, and a receiver module <b>106</b>. The transmitter module <b>102</b> is configured to transmit data over the transmission line <b>104</b> to the receiver module <b>106</b>. The transmitter module <b>102</b> includes data circuitry <b>108</b>, driver circuitry <b>110</b>, bias control <b>112</b>, and current sink <b>114</b>. The data circuitry <b>108</b> may be configured to accept digital data input and send corresponding data driver control signals to the driver circuitry <b>110</b>. The data driver control signals may be configured to control the driver circuitry <b>110</b> to transmit data over the transmission line <b>104</b>. The data to be transmitted by the driver circuitry <b>110</b> may correspond to the digital data input accepted by the data circuitry <b>108</b>.

The transmitter module <b>102</b> may receive power, in the form of electrical current, from a transmitter power supply VDD<b>2</b>. The transmitter power supply VDD<b>2</b> may be external to the transmitter module <b>102</b>. Likewise, the transmitter module <b>102</b> may be coupled with a transmitter ground node VSS<b>2</b>, which may be external to the transmitter module <b>102</b>.

The driver circuitry <b>110</b> may be configured to drive data signals across the transmission line <b>104</b>. The driver circuitry <b>110</b> may include low-swing high-speed differential line drivers configured to drive data signals using drive current across the transmission line <b>104</b> according to a differential signaling protocol. The data signals driven may be based on the data driver control signals received from the data circuitry <b>108</b>. The drive current may also be used to bias the transmission line <b>104</b> at a specified voltage range. The driver circuitry <b>110</b> may be configured to sink the drive current to the current sink <b>114</b>. The drive current may not be used for another purpose, thereby unnecessarily dissipating power.

The bias control <b>112</b> may be configured to control the magnitude of the drive current sinked by the current sink <b>114</b> from the driver circuitry <b>110</b> to the transmitter ground node VSS<b>2</b>. By controlling the magnitude of the drive current sinked by the current sink <b>114</b>, the bias control <b>112</b> may also control the bias conditions of the driver circuitry <b>110</b> and the transmission line <b>104</b>.

The receiver module <b>106</b> includes bias current source <b>116</b> and data circuitry <b>118</b>. The receiver module <b>106</b> may receive current from a bias power supply VDD<b>1</b> and may also be coupled with a receiver ground node VSS<b>1</b>. The bias power supply VDD<b>1</b> may also be known as a driver power supply. The bias current source <b>116</b> may be configured to source current from the bias power supply VDD<b>1</b> to the driver circuitry <b>110</b> via the transmission line <b>104</b>. The current drawn from bias power source VDD<b>1</b> via the transmission line <b>104</b> may be used by the driver circuitry <b>110</b> to transmit data over the transmission line <b>104</b>.

The data circuitry <b>118</b> may be configured to receive data signals from the transmission line <b>104</b>. The data circuitry <b>118</b> may be configured to process the received data signals to produce data output. The data circuitry <b>118</b> may be powered by a same bias power supply VDD<b>1</b> as the bias current source <b>116</b>. In some embodiments, the data circuitry <b>118</b> may be DC-coupled with the driver circuitry <b>110</b> via the transmission line <b>104</b>. In other embodiments, the data circuitry <b>118</b> may be AC-coupled with the driver circuitry <b>110</b> via the transmission line <b>104</b>.

<figref idref="DRAWINGS">FIG. 2</figref> is a schematic diagram illustrating communications interface circuitry <b>200</b>. The communications interface circuitry <b>200</b> includes a transmitter module <b>202</b>, associated circuitry <b>204</b>, and a termination load circuit <b>206</b>. The transmitter module <b>202</b> is an example of the transmitter module <b>102</b>, described with reference to <figref idref="DRAWINGS">FIG. 1</figref>. The transmitter module <b>202</b> may receive a data input signal, reference clock signal, and/or bias input signal from one or more other associated circuits such as associated circuits <b>208</b>, <b>210</b>, or <b>212</b>. Alternatively, the data input signal, reference clock signal, and/or bias input signal may be received from one or more other circuits external to the transmitter module <b>202</b>.

The associated circuitry <b>204</b>. may include a variety of electronic circuits such as associated circuits <b>208</b>, <b>210</b>, and <b>212</b>. The associated circuitry <b>204</b> may include memory, digital-to-analog converter (DAC), analog-to-digital converter (ADC), clock circuits, and so forth which may be coupled with, integrated with, or used in conjunction with the transmitter module <b>202</b>. The associated circuits <b>208</b>, <b>210</b>, and <b>212</b> may receive current from a transmitter power supply VDD<b>2</b> and be coupled with a common ground. The transmitter module <b>202</b> and the associated circuitry <b>204</b> may share the transmitter power supply VDD<b>2</b> and the common ground. The transmitter power supply VDD<b>2</b> may be provided by an external power source which is-not integrated with the transmitter module <b>202</b> or the associated circuitry <b>204</b>. In various embodiments, the transmitter power supply VDD<b>2</b> may be approximately 3.3 volts (V) or approximately 1.8 V. The common ground may be coupled with transmitter ground node VSS<b>2</b>, described with reference to <figref idref="DRAWINGS">FIG. 1</figref>.

The transmitter module <b>202</b> includes data circuitry <b>214</b>, phase locked loop (PLL) <b>216</b>, pre amp <b>218</b>, source transmitter <b>220</b>, and bias control <b>222</b>. The PLL <b>216</b> and the data circuitry <b>214</b> may together be an example of the data circuitry <b>108</b>, described with reference to <figref idref="DRAWINGS">FIG. 1</figref>. The pre amp <b>218</b> and source transmitter <b>220</b> may together be an example of the driver circuitry <b>110</b>, described with reference to <figref idref="DRAWINGS">FIG. 1</figref>. The bias control <b>222</b> may be an example of the bias control <b>112</b>, described with reference to <figref idref="DRAWINGS">FIG. 1</figref>.

The data circuitry <b>214</b> may be configured to read and process the data input according to a data clock signal received from the PLL <b>216</b>. The PLL <b>216</b> may be configured to receive an input reference clock signal and provide the data clock signal to the data circuitry <b>214</b>. The data clock signal may correspond to the input reference clock signal. In an embodiment including a differential signaling protocol, the data circuitry <b>214</b> may provide differential data signals, Data+ and Data−, to the pre amp <b>218</b>. The differential data signals may correspond to the data input signal received and processed by the data circuitry <b>214</b>. The differential data signals may be configured to control the pre amp <b>218</b> and source transmitter <b>220</b> to generate the corresponding data signals transmitted over the signal transmission lines TXN and TXP. Signal transmission lines TXN and TXP may be examples of the transmission line <b>104</b>, described with reference to <figref idref="DRAWINGS">FIG. 1</figref>.

The termination load circuit <b>206</b> is an example of the bias current source <b>116</b>, described with reference to <figref idref="DRAWINGS">FIG. 1</figref>. The termination load circuit <b>206</b> may be integrated with the transmitter module <b>202</b>. Alternatively, the termination load circuit <b>206</b> may be integrated with a receiver module, such as the receiver module <b>106</b>, described with reference to <figref idref="DRAWINGS">FIG. 1</figref>. The termination load circuit <b>206</b> may be configured to provide a bias current to the signal transmission lines TXN and TXP and the source transmitter <b>220</b>. The termination load circuit <b>206</b> includes a load resistor RO connected between the signal transmission line TXN and bias power supply VDD<b>1</b>. The termination load circuit <b>206</b> also includes a load resistor R<b>1</b> connected between the signal transmission line TXP and bias power supply VDD<b>1</b>. The bias power supply VDD<b>1</b> may also be referred to as a driver power supply. The bias power supply VDD<b>1</b> may include a 3.3 V power supply. The bias power supply VDD<b>1</b> may be associated with a receiver module, such as the receiver module <b>106</b>, described with reference to <figref idref="DRAWINGS">FIG. 1</figref>. The bias power supply VDD<b>1</b> may be provided by an external power supply which is not integrated with a transmitter module or a receiver module. In some embodiments, the bias power supply VDD<b>1</b> may be the same as the transmitter power supply VDD<b>2</b>.

The source transmitter <b>220</b> includes differential drivers NL<b>0</b> and NL<b>1</b> whose sources are connected. The differential drivers NL<b>0</b> and NL<b>1</b> may be approximately matched to one another in their design and/or performance. The drain of differential driver NL<b>0</b> is coupled with signal transmission line TXN. Likewise, the drain of differential driver NL<b>1</b> is coupled with signal transmission line TXP. The differential driver NL<b>0</b> may be configured to drive the signal transmission line TXN according to the Data− driving signal that is input to the gate of the differential driver NL<b>0</b> from the pre amp <b>218</b>. Likewise, differential driver NL<b>1</b> may be configured to drive the signal transmission line TXP according to Data+ driving signal that is input to the gate of the differential driver NL<b>1</b> from the pre amp <b>218</b>. The transmitter module <b>202</b> may be configured such that data signals driven on signal transmission lines TXN and TXP are complementary to one another for improved performance.

The source transmitter <b>220</b> may be configured such that the differential drivers NL<b>0</b> and NL<b>1</b> draw current from the bias power source VDD<b>1</b> through an impedance such as load resistors R<b>0</b> and R<b>1</b>, respectively. The source transmitter <b>220</b> and the termination load circuit <b>206</b> may be configured such that a voltage on the signal transmission line TXN swings between a high voltage and a low voltage to transmit data to the receiver. A voltage on the signal transmission line TXP may swing between a low voltage and a high voltage in a complementary fashion to the voltage swing on the signal transmission line TXN. The signal swing between the high and low voltages of signal transmission lines TXN and TXP are less than the voltage difference between the bias power supply VDD<b>1</b> and ground.

The transmitter module <b>202</b> may draw an approximately constant drive current I_drvthrough the differential drivers NL<b>0</b> and NL<b>1</b> as data is transmitted over the signal transmission lines TXN and TXP. The approximately constant drive current I_drvmay then be sinked to ground by the ground connection of a bias device NB<b>0</b>. The bias device NB<b>0</b> may control a value of the drive current I_drvvia a bias control signal received from a bias supply device NS<b>0</b>. The value of the drive current I_drvmay determine the bias conditions of the signal transmission lines TXN and TXP.

The bias control <b>222</b> may be configured to control the magnitude of the drive current I_drv, and consequently, the bias conditions of the source transmitter <b>220</b> and the transmission lines TXN and TXP. The bias control <b>222</b> may generate the bias supply signal and the bias on switch signal in response to the bias input signal and provide the bias supply signal and the bias on switch signal to the bias supply device NS<b>0</b>. In response to the bias supply signal and the bias on switch signal, the bias supply device NS<b>0</b> may control the bias device NB<b>0</b> which in turn controls the magnitude of the drive current I_drvand the bias conditions of the source transmitter <b>220</b> and the transmission lines TXN and TXP.

This approximately constant drive current I_drvconsumes power. A portion of the consumed power is used to switch the differential drivers NL<b>0</b> and NL<b>1</b>, while the majority of the rest of the power is consumed in establishing the DC bias conditions of the differential drivers NL<b>0</b> and NL<b>1</b>. The DC bias conditions may be configured to bias the signal transmission lines TXN and TXP at or about a nominal voltage. The DC bias conditions may also be configured to establish an approximately constant drive current I_drvthroughout data transmission over the signal transmission lines TXN and TXP.

A significant amount of power is dissipated in establishing the DC bias conditions without being used for another purpose. For example, the approximately constant drive current I_drvmay be nominally between approximately 10 milliamps (mA) and 24 mA. The signal swing across the load resistors R<b>0</b> and R<b>1</b> may be between approximately 0.4 and 0.6 volts (V). The remaining 2.7 V of power from a 3.3 V power supply may be dissipated in establishing DC conditions of the differential drivers NL<b>0</b> and NL<b>1</b>.

<figref idref="DRAWINGS">FIG. 3</figref> is a block diagram illustrating an exemplary communications interface <b>300</b> configured to re-use current from biasing a transmission line and/or driver circuitry to power a communications transmitter. The communications interface <b>300</b> may be configured to accept digital data input at a transmitter module <b>302</b>, transmit a representation of the digital data over the transmission line <b>104</b> to a receiver module <b>304</b>, and provide corresponding digital data output at the receiver module <b>304</b>. The communications interface <b>300</b> may comply with any HDMI standard such as HDMI 1.2. The communications interface <b>300</b> may also comply with any DVI standard, any DisplayPort standard, or any other video interface standard.

The communications interface <b>300</b> is similar to the communications interface <b>100</b> illustrated in <figref idref="DRAWINGS">FIG. 1</figref> except that the communications interface <b>300</b> is configured to power the transmitter module <b>302</b> by re-using current from the bias power supply VDD<b>1</b> provided over the transmission line <b>104</b> by the bias current source <b>116</b>. To accomplish this power re-use, the current sink <b>114</b> of the communications interface <b>100</b> is replaced by a combination of a current regulator <b>306</b> and a voltage regulator <b>308</b> in the communications interface <b>300</b>.

The current regulator <b>306</b> and the voltage regulator <b>308</b> may use drive current from the driver circuitry <b>110</b> to bias the transmission line <b>104</b> at an approximate bias voltage. The current regulator <b>306</b> may be configured to regulate the drive current drawn through the driver circuitry <b>110</b> to be approximately constant. The bias control <b>112</b> may be coupled with the current regulator <b>306</b> and configured to control the bias of the transmission line <b>104</b> via the current regulator <b>306</b>.

The voltage regulator <b>308</b> may be coupled with the current regulator <b>306</b> and configured to receive a regulated current from the current regulator <b>306</b>, regulate a voltage V_dd2on a regulated power supply output VDD<b>2</b> from VR to be approximately constant, and use the regulated current received from the current regulator <b>306</b> to provide power via the regulated power supply output VDD<b>2</b> from VR. While a voltage on the bias power source VDD<b>1</b> may be approximately 3.3 V, the regulated voltage on the regulated power supply output VDD<b>2</b> from VR may be approximately 1.8 V. Some electronic circuits of the transmitter module <b>302</b> may be configured to be powered, at least in part, by the regulated power supply output VDD<b>2</b> from VR of the voltage regulator <b>308</b>.

The data circuitry <b>108</b> configured for digital data communications may be coupled with the driver circuitry <b>110</b>. The data circuitry <b>108</b> may be configured to control the driver circuitry <b>110</b> to transmit data over the transmission line <b>104</b> according to digital data input. The data circuitry <b>118</b> configured for digital data communications may be coupled with the transmission line <b>104</b>. The data circuitry <b>118</b> may receive data signals from the transmission line <b>104</b> and produce a data output corresponding to the transmitted data.

In some embodiments, the data circuitry <b>118</b> may be DC-coupled with the driver circuitry <b>110</b> via the transmission line <b>104</b>. In other embodiments, the data circuitry <b>118</b> may be AC-coupled with the driver circuitry <b>110</b> via the transmission line <b>104</b>. In some embodiments, the data circuitry <b>118</b> may be powered by a same bias power supply VDD<b>1</b> as the bias current source <b>116</b>.

<figref idref="DRAWINGS">FIG. 4</figref> is a block diagram illustrating an alternative embodiment of a communications interface <b>400</b> configured to re-use current from biasing a transmission line and/or driver circuitry to power a communications transmitter. The communications interface <b>400</b> includes the transmitter module <b>302</b>, the bias current source <b>116</b>, the transmission line <b>104</b>, and a receiver module <b>402</b>. The receiver module <b>402</b> includes the data circuitry <b>118</b>. The communications interface <b>400</b> is similar to the communications interface <b>300</b> illustrated in <figref idref="DRAWINGS">FIG. 3</figref>, except that the bias current source <b>116</b> may be coupled with the driver circuitry <b>110</b> and the transmission line <b>104</b> on the same side as the transmitter module <b>302</b>, instead of on the same side as the receiver module <b>304</b>, as illustrated in <figref idref="DRAWINGS">FIG. 3</figref>. In the communications interface <b>400</b>, the bias current source <b>116</b> may be integrated with the transmitter module <b>302</b>. The bias current source <b>116</b> may receive power from a bias power supply VDD<b>1</b> while the data circuitry <b>118</b> may be powered by a receiver power supply VDD<b>3</b>. The receiver module <b>402</b> may be AC-coupled with the transmitter module <b>302</b>.

<figref idref="DRAWINGS">FIG. 5</figref> is a schematic diagram illustrating communications interface circuitry <b>500</b> configured to re-use current from transmission line biasing circuitry to power communications transmitter circuitry. The communications interface circuitry <b>500</b> is an improvement over the communications interface circuitry <b>200</b>, described with reference to <figref idref="DRAWINGS">FIG. 2</figref>. The communications interface circuitry <b>500</b> may be implemented as a system on chip (SOC) or chips on board (COB). The communications interface circuitry <b>500</b> includes a transmitter module <b>502</b>, associated circuitry <b>504</b>, the termination load circuit <b>206</b>, a start-up circuit <b>506</b>, and a re-used power supply <b>508</b>. The transmission line biasing circuitry may include at least the termination load circuit <b>206</b>.

The re-used power supply <b>508</b> includes a current sensor/control <b>510</b>, an optional voltage booster <b>512</b>, and a voltage regulator <b>514</b>. The re-used power supply <b>508</b> may be configured to sink a drive current I_drvfrom the source transmitter <b>220</b> into the current sensor/control <b>510</b> and provide a regulated power supply output VDD<b>2</b> from VR from the voltage regulator <b>514</b>. The current sensor/control <b>510</b> may include elements configured to sense and control current magnitudes according to a bias control signal received from a bias supply device NS<b>0</b>.

The regulated power supply output VDD<b>2</b> from VR may be used to power various circuits of the transmitter module <b>502</b> and the associated circuitry <b>504</b>. For example, the bias control <b>222</b>, the PLL <b>216</b>, the data circuitry <b>214</b>, the pre amp <b>218</b>, the associated circuit <b>208</b>, the associated circuit <b>210</b>, and the associated circuit <b>212</b> may be powered by the regulated power supply output VDD<b>2</b> from VR. If the power available from the regulated power supply output VDD<b>2</b> from VR is not sufficient to power all the various circuits of the transmitter module <b>502</b> and the associated circuitry <b>504</b>, an additional power source may be used to supplement the regulated power supply output VDD<b>2</b> from VR.

The regulated power supply output VDD<b>2</b> from VR may have a voltage approximately equal to a voltage of the bias power supply VDD<b>1</b> minus a voltage swing at the signal transmission lines TXN and TXP. The regulated power supply output VDD<b>2</b> from VR may provide a current up to approximately the value of the drive current I_drvfrom the source transmitter <b>220</b>. In some embodiments, the drive current I_drvmay be in a range between approximately 10 mA and 24 mA. For embodiments where an output voltage from the regulated power supply output VDD<b>2</b> from VR is required to be greater than a voltage available at the output of the current sensor/control <b>510</b>, the re-used power supply <b>508</b> may include the voltage booster <b>512</b> configured to boost the output voltage to a required level above the voltage available at the output of the current sensor/control <b>510</b>. For example, where the output voltage from the regulated power supply output VDD<b>2</b> from VR is required to be greater than 1.8 V and the voltage available at the output of the current sensor/control <b>510</b> is only 1.8 V, the re-used power supply <b>508</b> may include the voltage booster <b>512</b> configured to boost the output voltage to a required level above 1.8 V.

The communications interface circuitry <b>500</b> may be implemented using a differential signaling protocol such as used in a DC-coupled Transmission Minimized Differential Signaling (TMDS) data link. An HDMI or DVI link may be an example of a TMDS data link. For example, four channels may be implemented in parallel (not shown), with each channel having a drive current of approximately 10 mA. The total drive current drawn from the bias power source VDD<b>1</b> from the four channels may be approximately 40 mA. The bias power source VDD<b>1</b> may provide a voltage of approximately 3.3 V. A voltage on the signal transmission lines TXN and TXP may be modulated by the differential drivers NL<b>0</b> and NL<b>1</b> to have a voltage swing of approximately 0.4 V to 0.6 V. For a four-channel communications interface circuitry configured to provide a swing of approximately 0.6 V and a current of approximately 10 mA per channel, the drive current I_drvat the interconnected sources of differential drivers NL<b>0</b> and NL<b>1</b> for all four channels may provide a power source having a current of approximately 40 mA and a voltage of approximately 1.8 V. This power source may allow the drive current I_drvto be re-used via the re-used power supply <b>508</b> to provide the regulated power supply output VDD<b>2</b> from VR.

The start-up circuit <b>506</b> may be configured to provide a start-up current to the re-used power supply <b>508</b> as the communications interface circuitry <b>500</b> powers up before the source transmitter <b>220</b> provides an approximately constant drive current I_drv. Because the transmitter module <b>502</b> may be configured to receive power from the regulated power supply output VDD<b>2</b> from VR, the differential drivers NL<b>0</b> and NL<b>1</b> may remain in an off state until after the regulated power supply output VDD<b>2</b> from VR reaches a steady state operating voltage V_dd2. The start-up circuit <b>506</b> may provide the start-up current to the re-used power supply <b>508</b> when the source transmitter <b>220</b> does not provide the approximately constant drive current I_drv. The re-used power supply <b>508</b> may then use the start-up current to provide a regulated power supply output VDD<b>2</b> from VR to the various circuits of the communications interface circuitry <b>500</b> that are configured to be powered by the regulated power supply output VDD<b>2</b> from VR as the communications interface circuitry <b>500</b> first begins operating. The start-up circuit <b>506</b> may include a resistor R<b>2</b> connected between signal transmission line TXP and a connection point, a resistor R<b>3</b> connected between signal transmission line TXN and the connection point, and a resistor R<b>4</b> connected between ground and the connection point. A diode D<b>0</b> may be connected between the connection point and the current sensor/control <b>510</b>.

In some embodiments, the termination load circuit <b>206</b> may be integrated with a receiver module (not shown), the start-up circuit <b>506</b> may be integrated with the transmitter module <b>502</b>, and the transmission lines TXN and TXP may be at least partially incorporated within a cable such as an HDMI cable. In these embodiments, the transmitter module <b>502</b> may be in an unpowered state when the cable is not coupled with both the transmitter module <b>502</b> and the receiver module. When the receiver module is in a powered-up state, and the cable is first attached to couple the receiver module with the transmitter module <b>502</b>, the start-up circuit <b>506</b> may be operational to power up the transmitter module <b>502</b> using power received from the receiver module over the transmission lines TXN and TXP. In other embodiments where the termination load circuit <b>206</b> is coupled with the transmitter module <b>502</b> via the transmission lines TXN and TXP, and both the termination load circuit <b>206</b> and the transmitter module <b>502</b> are in an unpowered state, the start-up circuit <b>506</b> may function in a similar manner when the termination load circuit <b>206</b> first powers up.

The start-up circuit <b>506</b> may be configured to draw a small current from the termination load circuit <b>206</b> and provide a start-up current to the current sensor/control <b>510</b>. The start-up current may be relatively small compared to the steady state drive current I_drv. This start-up current may begin to be provided approximately at the same time as the signal transmission lines TXN and TXP are connected to the termination load circuit <b>206</b>, or the termination load circuit <b>206</b> begins receiving power from the bias power supply VDD<b>1</b>. After the transmitter module <b>502</b> reaches full operational status, the signal transmission lines TXN and TXP may become biased and an approximately constant drive current I_drvmay flow from the source transmitter <b>220</b> into the re-used power supply <b>508</b>. The start-up current may then no longer be needed by the re-used power supply <b>508</b> to provide the regulated power supply output VDD<b>2</b> from VR, and the start-up circuit <b>506</b> may reduce the start-up current to essentially zero or a negligible value in comparison to the drive current I_drv.

<figref idref="DRAWINGS">FIG. 6</figref> is a schematic diagram illustrating exemplary circuitry <b>600</b> configured to re-use current from biasing circuitry as a second power supply. The circuitry <b>600</b> includes the source transmitter <b>220</b>, the start-up circuit <b>506</b>, and the re-used power supply <b>508</b>. The source transmitter <b>220</b> may provide an approximately constant drive current I_drvto the re-used power supply <b>508</b>. For example, the drive current I_drvmay be approximately 10 mA for a single channel communications interface, or 40 mA for a four channel communications interface. As another example, the drive current I_drvmay be approximately 24 mA for a single channel communications interface, or 48 mA for a two channel communications interface.

The re-used power supply <b>508</b> includes voltage controlled current sources G<b>1</b> and G<b>2</b>. Voltage controlled current sources G<b>1</b> and G<b>2</b> may also be configured to sense current. Voltage controlled current source G<b>1</b> has a gain gm that is proportional to one (1), while voltage controlled current source G<b>2</b> has a gain g. that is proportional to N−1. The gain (g_m) ratio provided by the pair of voltage controlled current sources G<b>1</b> and G<b>2</b> is therefore 1:N−1. The voltage controlled current source G<b>1</b> may act as a reference current sensor and control.

A fixed current source <b>604</b> is coupled with the voltage controlled current source G<b>1</b> and configured to draw a current I_dc=I_drv/N. A shunt regulator <b>602</b> is provided with a shunt regulator control input port coupled with the fixed current source <b>604</b> at one end. The fixed current source <b>604</b> is also coupled with the voltage controlled current source G<b>1</b> at the same end. The shunt regulator control input port senses a voltage provided by the fixed current source <b>604</b> between the shunt regulator control input port and ground. The shunt regulator <b>602</b> is configured to set a voltage at a shunt regulator input port to equal the voltage at the shunt regulator control input port by shunting current from the voltage controlled current source G<b>2</b> through the shunt regulator input port. The current passing through the voltage controlled current source G<b>2</b> may be approximately N−1 times the reference current passing through voltage controlled current source G<b>1</b>. Therefore, the current passing through the voltage controlled current source G<b>2</b> may be approximately (N−1)·(I_drv/N). Those skilled in the art will recognize that there may be many different gains defined for voltage controlled current source G<b>1</b> and voltage controlled current source G<b>2</b> that will perform the intended function of various embodiments.

Voltage controlled current sources G<b>1</b> and G<b>2</b> may be coupled with other elements of the current sensor/control <b>510</b>, the re-used power supply <b>508</b>, and/or the communications interface circuitry <b>500</b> via optional impedances Z<b>1</b>, Z<b>2</b>, Z<b>3</b>, Z<b>4</b>, Z<b>5</b>, Z<b>6</b>, Z<b>7</b>, and Z<b>8</b>. Voltage controlled current sources G<b>1</b> and G<b>2</b> may include MOSFET or BJT devices. In some embodiments, the re-used power supply <b>508</b> may be configured with more than two voltage controlled current sources G<b>1</b> and G<b>2</b>.

After the circuitry <b>600</b> reaches steady state and the start-up circuit <b>506</b> is no longer providing a significant start-up current, the drive current I_drvmay be approximately equal to the sum of the current passing through the voltage controlled current sources G<b>1</b> and G<b>2</b>. The current passing through voltage controlled current source G<b>2</b>, which is approximately ((N−1)/N)·I_drv, may be available to be output from the current sensor/control <b>510</b> to the voltage regulator <b>514</b>. The voltage regulator <b>514</b> may then regulate a voltage of the regulated power supply output VDD<b>2</b> from VR. The regulated power supply output VDD<b>2</b> from VR may then provide power including up to approximately ((N−1)/N)·I_drvamps of current at the regulated voltage V_dd2to circuitry of the transmitter module <b>502</b> and the associated circuitry <b>504</b>.

In some embodiments, the voltage booster <b>512</b> may be disposed between the current sensor/control <b>510</b> and the voltage regulator <b>514</b>. The voltage booster <b>512</b> may be configured to increase a voltage output from the current sensor/control <b>510</b>, and consequently, the regulated voltage V_dd2at the regulated power supply output VDD<b>2</b> from VR. The voltage booster <b>512</b> may be useful to enable the re-used power supply <b>508</b> to provide the regulated voltage V_dd2which is at a higher voltage than the voltage output from the current sensor/control <b>510</b>.

<figref idref="DRAWINGS">FIG. 7</figref> is a block diagram illustrating DC-coupled communications interface circuitry <b>700</b> configured to re-use current from transmission line biasing circuitry to power communications transmitter circuitry. The DC-coupled communications interface circuitry <b>700</b> includes a transmitter module <b>702</b>, signal transmission lines TXN and TXP, and a receiver module <b>704</b>. The transmitter module <b>702</b> may be an example of the transmitter module <b>502</b>, described with reference to <figref idref="DRAWINGS">FIG. 5</figref>. The transmitter module <b>702</b> may include the source transmitter <b>220</b> and the re-used power supply <b>508</b>. The receiver module <b>704</b> may include the termination load circuit <b>206</b> and data circuitry <b>706</b>. The data circuitry <b>706</b> may be an example of the data circuitry <b>118</b>, described with reference to <figref idref="DRAWINGS">FIG. 1</figref>. The termination load circuit <b>206</b> and the data circuitry <b>706</b> may both receive power from a bias power supply VDD<b>1</b>.

The source transmitter <b>220</b> may be configured to drive data signals across the signal transmission lines TXN and TXP to the data circuitry <b>706</b>. The data circuitry <b>706</b> may be DC-coupled with the source transmitter <b>220</b> via the signal transmission lines TXN and TXP. The source transmitter <b>220</b> may be configured to draw a combined current equal to approximately I_drvfrom the termination load circuit <b>206</b>, and provide a drive current I_drvto the re-used power supply <b>508</b>. The re-used power supply <b>508</b> may be configured to provide the regulated power supply output VDD<b>2</b> from VR to a variety of circuits associated with the transmitter module <b>702</b>.

<figref idref="DRAWINGS">FIG. 8</figref> is a block diagram illustrating AC-coupled communications interface circuitry <b>800</b> configured to re-use current from transmission line biasing circuitry to power communications transmitter circuitry. The AC-coupled communications interface circuitry <b>800</b> includes a transmitter module <b>802</b>, signal transmission lines TXN and TXP, and a receiver module <b>804</b>. The transmitter module <b>802</b> may be an example of the transmitter module <b>502</b>, described with reference to <figref idref="DRAWINGS">FIG. 5</figref>. The transmitter module <b>802</b> may include the source transmitter <b>220</b>, the termination load circuit <b>206</b>, and the re-used power supply <b>508</b>. The receiver module <b>804</b> may include data circuitry <b>806</b> configured to receive power from a receiver power supply VDD<b>3</b>. The data circuitry <b>806</b> may be an example of the data circuitry <b>118</b>, described with reference to <figref idref="DRAWINGS">FIG. 1</figref>. The termination load circuit <b>206</b> may be configured to receive power from a bias power supply VDD<b>1</b>.

The AC-coupled communications interface circuitry <b>800</b> is similar to the DC-coupled communications interface circuitry <b>700</b> except that the source transmitter <b>220</b> may be AC-coupled with the data circuitry <b>806</b> via the signal transmission lines TXN and TXP, and the termination load circuit <b>206</b> may be integrated with the transmitter module <b>802</b>.

<figref idref="DRAWINGS">FIG. 9</figref> is a flowchart of an exemplary method for powering circuits for a communications interface. The communications interface may transmit video data over a transmission line from a communications transmitter module to a communications receiver module for display on a video display. In the method, circuitry associated with the communications transmitter module, such as transmitter module <b>302</b>, may be powered using current drawn from a communications receiver module, such as the receiver module <b>304</b>, over a transmission line, such as transmission line <b>104</b>. By powering the circuitry associated with the communications transmitter module using current drawn from the communications receiver module, less power overall may be consumed by the communications transmitter module. The current drawn from the communications receiver module may need to be drawn at least for the purpose of biasing the transmission line and/or communications interface circuitry. Re-using the current drawn to at least partially power the transmitter module reduces an amount of additional power needed to power the transmitter module, and therefore, reduces overall power consumption.

In step <b>902</b>, a transmission line is biased using biasing circuitry coupled with the transmission line. The biasing circuitry may be configured to draw current from a first power supply. The biasing circuitry may be configured to bias the transmission line at a preset nominal voltage. The biasing circuitry may also be configured to cause a preset nominal value of current to flow through the transmission line. The first power supply may also be used to power circuitry of the communications receiver module. The circuitry of the communications receiver module may also be coupled with the transmission line.

In step <b>904</b>, current from the first power supply is sinked through biasing circuitry. Circuitry including a current regulator may be used to sink the current. The current regulator may be configured to regulate the current sinked from the first power supply through the biasing circuitry to be approximately constant. The circuitry used to sink the current may also include a voltage regulator configured to regulate voltage of a second power supply.

In step <b>906</b>, a voltage of the second power supply is regulated to be approximately constant. The second power supply may include a voltage regulator configured to receive at least a portion of the current sinked in step <b>904</b> as well as regulate the voltage of the second power supply.

In step <b>908</b>, at least a portion of the current sinked from the first power supply in step <b>904</b> is supplied to the circuitry associated with the communications transmitter module via the second power supply. The voltage regulator as described in step <b>906</b> may supply at least a portion of the current sinked in step <b>904</b> to circuitry associated with the communications transmitter module configured to be powered by the second power supply. The current supplied to the circuitry associated with the communications transmitter module may be used to power the communications transmitter module.

The circuitry associated with the communications transmitter module may be configured to be powered by a combination of power from the second power supply and a third power supply. For example, the circuitry associated with the communications transmitter module may require more power than the second power supply may be able to provide. By receiving power from a combination of the second power supply and the third power supply, the circuitry associated with the communications transmitter module may consume less power overall than if the third power supply alone powered the circuitry associated with the communications transmitter module.

Several embodiments are specifically illustrated and/or described herein. However, it will be appreciated that modifications and variations are covered by the above teachings and within the scope of the appended claims without departing from the spirit and intended scope thereof. For example, embodiments of the present invention may be used in other applications besides data communications systems to power an electronic circuit using current also used to bias a voltage node at approximately a specific voltage value. Embodiments of the present invention may be used to power integrated circuits (IC's), system on chips (SOC's), or chips on boards (COB's). Embodiments of the present invention may also be used to power an electronic circuit using current which is also used to produce a voltage drop across a circuit element, such as a resistor, coupled with another electronic circuit. In some embodiments, analog signals may be communicated over a transmission line between a transmitter and receiver in addition to or instead of digital data.

The embodiments discussed herein are illustrative of the present invention. As these embodiments of the present invention are described with reference to illustrations, various modifications or adaptations of the methods and or specific structures described may become apparent to those skilled in the art. All such modifications, adaptations, or variations that rely upon the teachings of the present invention, and through which these teachings have advanced the art, are considered to be within the spirit and scope of the present invention. Hence, these descriptions and drawings should not be considered in a limiting sense, as it is understood that the present invention is in no way limited to only the embodiments illustrated.